1. Field of the Invention
The present invention relates to a method and apparatus for effecting automatic ventricular defibrillation and/or demand cardioversion through the means of an implanted automatic defibrillator. More particularly, the invention relates to an implantable device responsive to ventricular fibrillation for automatically defibrillating a patient, and further responsive to a simulated fibrillation signal to become a demand cardioversion device capable of treating non-lethal arrhythmias.
2. Description of the Prior Art
There continues to be a need for devices which, automatically or upon demand, as the case may be, rapidly and efficiently perform defibrillation and/or cardioversion functions in order to correct any one of a number of lethal and non-lethal arrhythmic heart conditions, including atrial tachycardia, atrial flutter, atrial fibrillation, junctional rhythms, ventricular tachycardia, ventricular flutter, and ventricular fibrillation, as well as any other non-pacing related arrhythmic condition correctable by applying electric shocks to the heart.
Past efforts have included the development of a command atrial cardioverting device, such as is disclosed in U.S. Pat. No. 3,952,750 to Mirowski et al, for the treatment of non-lethal arrhythmias. Such a device provides correction of atrial fibrillation, flutter or tachycardia by two alternative techniques: command by the patient using a magnet to cause closure of a relay beneath the surface of the skin so as to effect the needed cardioversion; or command by a physician who operates a command device to transmit command signals received by a miniature receiver located in the cardioversion device implanted in the patient. As further disclosed in the aforementioned patent, the cardioversion device then synchronously (that is, in synchronization with the QRS complex as detected by an ECG monitor) cardioverts the heart.
Another development in the treatment of heart disease consists of the method and apparatus for monitoring heart activity and for automatically treating lethal arrhythmias. Examples of a recent method and apparatus are disclosed in copending applications of Langer et al, U.S. Ser. Nos. 878,005 and 878,006, now U.S. Pat. Nos. 4,202,340 and 4,184,493, respectively. These applications disclose a highly sophisticated technique for detecting and reacting to ventricular fibrillation, entailing sensing ECG signals from the heart, shaping of such signals, performing a discrimination function and an averaging function relative to the shaped signals, examining the averaged signals to determine whether predetermined threshold limits are met, and then effecting defibrillation if the predetermined threshold limits are not met.